This invention relates to measurements of clearances, and more specifically, to an apparatus and method for measuring or selectively adjusting a clearance between two objects such as a stationary object and a rotating object.
Rotating systems typically have clearances or gaps to avoid contact or rubs during operation due to manufacturing tolerances and thermal expansion or mechanical strain effects. Undesirably, clearances generally result in loss of efficiency of the system. For example, in a pressurized system, clearances cause loss in efficiency due to blowby or degradation of pressure ratios. Typically, manufacturing and design costs increase as attempts are made to reduce the size of clearances in a system.
In a jet turbine engine, for example, a clearance exists between the thin-walled casing and the tips of the rotor blades. The thin walled casing is designed so that during operation it can be heated or cooled to vary the size of the clearance between the casing and the tip of the blade particularly during start-up and shutdown. Rotating systems having a thick casing, however, can not be readily resized by heating or cooling the thick casing to adjust the clearance between the casing and a rotor blade tip.
Therefore, there is a need for a low cost, on-line apparatus and method for measuring a clearance between objects and selectively adjusting and optimizing the clearance during operation.
The above-mentioned need is met by the present invention which in one aspect relates to a technique for measuring a clearance between a surface of a first object and a surface of a second object. The system includes a sensor for sensing within a field of view a portion of the second object and generating a signal in response thereto. The field of view varies in response to varying the clearance between the sensor and the second object. A controller determines a clearance between the surface of the first object and the surface of the second object in response to the signal.
The controller is operable to determine the clearance in response to a magnitude of the signal or in response to the signal comprising a plurality of signals. Advantageously, the second object is a rotating object and the portion of the second object has a varying pattern.
In another aspect of the present invention, a system for adjusting the clearance between a first object and a second object includes a movable seal disposed between the first object and the second object. A sensor is attachable to at least one of the first object and the seal for sensing within a field of view a portion of the second object and generating a signal in response thereto. A controller is operable to adjust a position of the seal relative to the second object to selectively adjust the clearance therebetween in response to the signal. Desirably, the seal is a segmented labyrinth seal having a thermally expandable portion. Advantageously, the second object is a rotating object and the portion of the second object has a varying pattern.
In another aspect of the present invention, a system is provided for measuring vibrations of an object. Desirably, a portion of the object includes a two-dimensional pattern of spaced-apart reflective elements.
In still another aspect of the present invention, a method for measuring a clearance between a surface of a first object and a surface of second object comprises the steps of sensing within a field of view a portion of the second object and generating a signal in response thereto, the field of view varying in response to varying the clearance between the first object and the second object, and determining the clearance between the first object and the second object in response to the signal.